EP2199753A2 - Fluid cylinder with a microwave measuring assembly and method for recording at least one parameter - Google Patents

Abstract

The cylinder (21) has a high frequency generator (11) supplying high-frequency signals to a microwave-coupling probe (19). An evaluation device detects a parameter by comparing the signals from the probe and signals produced from a waveguide shaft. A part of the evaluation device and high frequency lines are arranged on a board (10), where the lines are formed as conductor paths. A run time- measuring device (13) is arranged on the board for measuring board-humidity and propagation speed of the signals. The evaluation device corrects the parameter based on signals of the measuring device.

Description

The invention relates to a fluidic cylinder having a microwave measuring arrangement for detecting at least one parameter having the features of the preamble of claim 1.

Such a microwave measuring arrangement is for example from the DE 10205904 A1 , of the US-A 4588953 or the EP 1040316 B1 is known and used to capture parameters such as the piston position or the piston speed. RF signals are fed from an RF generator to the antenna or microwave coupling probe and from there back to an evaluation via electrical conductors. The propagation speed of the RF signals on HF lines exerts an influence on the measurement result, that is, if the electrical properties of the lines change, the measurement result is falsified. In one embodiment of these RF lines as printed conductors on a printed circuit board, these can change, in particular depending on moisture, in such a way that the dielectric properties are influenced. This leads to runtime errors of the RF signals and as a result to corrupted measurement results.

From the DE 10 2006 052 790 a position measuring device for determining the position of a test object is known in which microwaves are coupled out with the aid of an antenna body into a waveguide and coupled from the waveguide into the antenna body. The antenna body is made of a dielectric material, for example of a plastic, and isolates two pole faces from each other. In order to be able to determine the dielectric properties of the antenna body and to include them in the evaluation of the position signal, the antenna body has a plurality of resonant circuits on an end region facing the waveguide and at a maximum distance from the microwave generator, which can reflect a fraction of the microwaves emitted by the microwave generator almost loss-free. To determine the moisture-dependent dielectric constant of the antenna body, a microwave generated by the microwave generator is changed in its frequency until resonance occurs, so that based on the detected resonance frequency, the current dielectric constant of the antenna body can be determined.

It is therefore an object of the invention to compensate for or at least minimize run-time errors due to changes in the dielectric properties in order to obtain more accurate measurement results.

This object is achieved by a fluidic cylinder with a microwave measuring device having the features of claim 1.

In an advantageous manner, a transit time measuring device for detecting the moisture and / or propagation speed of the RF signals is arranged on the circuit board provided with the HF lines formed as strip conductors, by the changes of the propagation speed of the Detected RF signals as a result of changes in the dielectric properties and an evaluation can be supplied. Since this transit time measuring device is arranged on the same board, it is assumed that the entire board, for example, changes in all places in the same way as a function of moisture. The correction values detected by the transit time measuring device can then be used to correct the parameter measured values, that is to say, for example, position measured values or speed measured values. As a result, runtime errors can be compensated or minimized and exact measurement results can be achieved even with changing dielectric properties of the board, for example as a function of moisture.

The measures listed in the dependent claims advantageous refinements and improvements of the claim 1 arrangement are possible.

The evaluation device expediently has a phase and amplitude comparator and an associated microcontroller for evaluating the detected phase differences or amplitude ratios.

The arranged on the board phase and amplitude comparator is advantageously formed by interconnect elements and is designed in particular as a six-port circuit (six-port device). The determined correction values for propagation time changes thus have a direct effect on the evaluation signals of the phase and amplitude comparator.

In an expedient structural embodiment of the six-port circuit, this consists of three 90-degree hybrid couplers, a Wilkinson divider and a directional coupler, wherein power and / or level measuring devices for thereby formed, in each case in steps of 90 ° to each other staggered signals of the coupling probe running and are provided by the returning RF signals, which are connected to the microcontroller for evaluation. The 90-degree hybrid couplers preferably consist of four annular interconnected conductor track pieces each having a length of λ / 4. Such an arrangement can be produced simply and inexpensively as a simple printed conductor structure.

In the leading to the microwave coupling probe conductor for the RF signals, a directional coupler for decoupling a part of the outgoing and a part of the returning from the microwave coupling probe RF signals is arranged in an advantageous manner. Even such a directional coupler can be realized in a simple and cost-effective manner by interconnect elements.

In a further embodiment of the invention, in one of the two interconnects connecting the directional coupler to the phase and amplitude comparators, a delay device likewise designed as a conductor path for compensating the length of the interconnect between the directional coupler and the coupling probe for the two RF signals to be compared is arranged. This is a complementary measure to compensate for changes in the dielectric properties of the tracks, for example by exposure to moisture. This delay device can serve, for example, as a coarse alignment, while the transit time measuring device is particularly suitable for fine compaction, but also for sole compensation.

The transit time measuring device likewise consists advantageously of conductor track pieces, in particular of a measuring strip conductor piece, which has a coupling device for HF signals which is preferably connected to the HF generator Outcoupling device which is connected to a resonance measuring device.

The measuring conductor piece preferably has a length of λ / 2. In this case, the resonance measuring device advantageously has a level measuring device connected to the microcontroller, and the microcontroller has means for stepwise frequency change of the HF generator in order to be able to detect the respective resonance frequency. As a result, shifts of the resonant frequency can be detected, which is a measure of the changes in the dielectric properties of the measuring strip conductor, from which in turn the propagation speed or transit time of the RF signals can be derived on the board.

A further level measuring device connected to the microcontroller is provided for detecting the RF power fed into the transit time measuring device. By comparing the values of the two level measuring devices, further information about the exact delay compensation can be obtained.

A conductor path connecting the RF generator to the transit time measuring device expediently has a directional coupler for coupling out HF signals conducted to the microwave coupling probe.

To suppress undesired interference, the output signal of the HF generator is expediently passed through a harmonic filter.

Figur 1

ein Blockschaltbild einer auf einer Platine angeordneten Auswerteeinrichtung mit Laufzeit-Mess-einrichtung und HF-Generator, die mit einer Mikrowellen-Koppelsonde einer an einem fluidischen Zylinder angeordneten Mikrowellen-Messanordnung verbunden sind,

Figur 2

eine realitätsnahe Ausführung der in Figur 1 dargestellten elektronischen Komponenten, die auf der Platine angeordnet sind,

Figur 3

eine schematische Darstellung eines Phasen- und Amplitudenvergleichers als Bestandteil der in Figur 2 dargestellten Six-Port-Schaltung und

Figur 4

ein Signaldiagramm zur Erläuterung der Verschiebung der Resonanzfrequenz, die mittels der Laufzeit-Messeinrichtung zur weiteren Auswertung erfasst wird.

An embodiment of the invention is illustrated in the drawing and explained in more detail in the following description. Show it:

FIG. 1

a block diagram of an arranged on a board evaluation device with transit time measuring device and RF generator, which are connected to a microwave coupling probe arranged on a fluidic cylinder microwave measuring device,

FIG. 2

a realistic execution of the in FIG. 1 represented electronic components, which are arranged on the board,

FIG. 3

a schematic representation of a phase and amplitude comparator as part of in FIG. 2 illustrated six-port circuit and

FIG. 4

a signal diagram for explaining the shift of the resonance frequency, which is detected by means of the transit time measuring device for further evaluation.

In the in the FIGS. 1 and 2 illustrated embodiment are on a board 10, an RF generator 11 (high-frequency generator for microwave frequencies), a harmonic filter 12, a transit time measuring device 13, a directional coupler 14, a six-port circuit 9 (six-port device) and a microcontroller 18, the six-port circuit 9 consisting of a phase and amplitude comparator 17, a delay line formed as a delay device 16 and a further directional coupler 15. In the schematic block circuit according to FIG. 1 the harmonic filter 12 is not shown for simplicity. It serves to filter out interfering signals, whereby in a simpler embodiment it can also be dispensed with or else other interference suppression measures are provided. On the other hand, the microcontroller 18 is on as real version shown board 10 according to FIG. 2 not recognizable. It can be arranged for example on the back of this board or externally.

All line connections between the components are designed as strip conductors. The HF generator 11 is connected to the transit time measuring device 13, which will be explained in more detail later. A portion of the RF signals is coupled via the first directional coupler 14 in a leading to serving as an antenna microwave coupling probe 19 line. This line has at one end a connected to ground terminating resistor 20. A portion of the RF signals is then decoupled on the way to the microwave coupling probe 19 by means of the second directional coupler 15 and fed via the delay means 16 to the phase and amplitude comparator 17.

The microwave coupling probe 19 is arranged on an end region of a fluidic cylinder 21, which is usually designed as a cylinder cover, and is integrated in this cylinder cover, not shown in detail. In the cylinder 21, a piston 23 provided with a piston 23 is slidably guided. It can also be a rodless piston. About the microwave coupling probe 19, a microwave waveguide wave is coupled into the interior of the cylinder 21, which is reflected on the piston 23 and resumed by the microwave coupling probe 19, which then serves as a receiving antenna. These processes are described in detail in the prior art mentioned above.

The reflected and detected again by the microwave coupling probe 19 hollow shaft is returned as an RF signal again and partially coupled out by means of the second directional coupler 15 and fed to the phase and amplitude comparator 17. There is a phase or amplitude comparison between the running and returning RF signals instead, these measurements can be evaluated as a measure of the position of the piston 23 and its speed or acceleration. The measurement results are therefore supplied to the microcontroller 18. The evaluation of the phase difference for position determination of the piston 23 by means of a phase comparator is also described in detail in the prior art mentioned above.

The leading to the microwave coupling probe 19 line or conductor is connected to a contact surface 24 which is connected in a manner not shown via a pin or wire to the microwave coupling probe 19. This contact surface 24 is surrounded by a ground surface 25 which is connected to the metallic cylinder 21.

The phase and amplitude comparator 17, which serves for phase or amplitude comparison, is a component of in FIG. 2 illustrated six-port circuit 9 is in FIG. 3 schematically and in FIG. 2 represented in the form of printed conductors. Such six-port circuits containing a phase and amplitude comparator, which are often referred to as six-port devices in the literature, are for example out IEEE Transactions on Microwave Theory and Techniques, Vol. 12, pages 2414-2417 , or Vol. 47, no. 12, pages 2621-2624 , or Vol. MTT-23, no. 12, pages 978-984 , or Vol. MTT-25, no. 12, pages 1075-1083 , known and there in their function and mode of action, in particular with respect to the phase and amplitude comparison described in more detail. A detailed description of the mode of action can therefore be dispensed with here.

for measuring the reflection factor at the microwave coupling probe 19 or antenna for detecting the phase deviation Between the incoming and the returning wave, parts of the forward and backward signals are additively superimposed. Depending on the phase of these signals, constructive or destructive superimposition occurs, which leads to corresponding signal levels at the outputs of the six-port circuit 9. These signal levels are measured by means of detector circuits 26-29. These differently phase shifted and then superimposed signals are applied to the detector circuits 26-29 impedance matched. By this impedance matching, a better conversion factor of the detector can be achieved, which has a positive effect on the signal-to-noise ratio. Furthermore, the impedance matching avoids reflections at the detector circuits 26-29.

The six-port circuit 9 used in the exemplary embodiment consists of three 90-degree hybrid couplers 30-32, a Wilkinson divider 33 and the second directional coupler 15. Each 90-degree hybrid coupler 30-32 consists essentially of four ring-like interconnects each having a length of substantially λ / 4. A 90 degree hybrid coupler 30-32 splits an input signal into two output signals having equal amplitudes but whose phases have a 90 degree difference. A portion of the returning from the microwave coupling probe 19 signals is thereby fed via the Wilkinson divider 33, and a portion of the leading to the microwave coupling probe 19 signals is fed via the average 90grad hybrid coupler 31. At the second input of a grounded resistance 34 is connected. The signals to be compared with one another via the Wilkinson divider 33 and the 90-degree hybrid coupler 31 are then supplied to the two remaining 90-degree hybrid couplers 30 and 32 for additive superimposition, to whose outputs the detector circuits 26-29 are connected are. The superposition by the 90-degree hybrid couplers 30 and 32 is done so that at their outputs parts of the coupling probe 19 back and are superimposed by this returning signals, this superimposition takes place at the different outputs of the 90-degree hybrid coupler 30 and 32 but with different phase differences. These phase differences are preferably 0 degrees, 90 degrees, 180 degrees and 270 degrees. The amplitude at the outputs of the 90 degree hybrid couplers 30 and 32 is essentially determined by the phase difference resulting in constructive or destructive interference. The serving as a level or power detector detector circuits 26-29 lead to the microcontroller 18 at different frequencies measured levels, in which case the microprocessor can be closed by an algorithm on the piston position or piston speed, for example, in an intermediate step, the phase of the reflection factor on Antenna Cylinder System is calculated. An immediate phase measurement, as it takes place for example in known mixers, is no longer necessary. Amplifier modules can be omitted. The six-port circuit is a substantially linear element, which operates level-independent in contrast to the mixer. The circuit elements in the principle of the six-port circuit can be adapted to RF technically easier reflection, which leads to a better signal quality. Due to the simple design in printed circuit board technology, less stringent requirements are placed on printed circuit board technology, and a cheaper realization is possible.

A phase and amplitude comparator, which is constructed on a printed circuit board as an alternative to a six-port circuit with the aid of semiconductor diodes and line structures, also changes its measurement result as a function of the moisture content of the printed circuit board. However, in such a case, the measurement errors numerically much more difficult to handle, since the reflection factors of such semiconductor mixer of the oscillator amplitude Depending on the humidity and depending on the different frequencies, the products may spread differently and react with multiple reflections, thereby additionally influencing the measurement result.

With the six-port reflectometer or with the six-port circuit, there are no additional frequencies due to the linearity, which would have to be taken into account in the compensation. The reflection factors are constant over different amplitude values, unlike a semiconductor mixer, i. Compensation does not need to take into account the oscillator output level.

Since the running signals and the returning signals to the six-port circuit 9 must be performed over different lengths of interconnects, the delay device 16 is connected as a compensation device in the supply of the leading signal to the phase and amplitude comparator 17, in case of changes in the dielectric Properties to achieve a runtime compensation. If the dielectric behavior of the line is changed by moisture, the duration of this line changes. As a result, the phase and amplitude comparator sees a different phase angle of the reflection factor. The delay device 16 is exposed to the same humidity influences as the line between the directional coupler and microwave coupling probe, that is, the propagation speed on this line changes in the same manner as that on the line between the microwave coupling probe 19 and the directional coupler 15 Signals in each case twice over the line between directional coupler 15 and microwave coupling probe 19, namely back and forth. By suitably selected length of the delay device 16 or delay line can be achieved that cancel the effects of moisture.

However, this moisture compensation by the delay 16 has its limits. Although it can be achieved that occasionally the moisture compensation succeeds or succeeds on average, but can not be used for all possible due to the imperfection of the line circuits, as used in the phase and amplitude comparator 17 and the six-port circuit 9 Reflection factors an ideal compensation can be achieved, that is, the delay means 16 can only represent a coarse compensation. The remaining moisture dependencies and dependencies of geometry changes are too complicated to be corrected by simple circuit measures. For this purpose, however, the microcontroller must have information about the current runtime behavior of the printed conductors. He gets this via the transit time measuring device 13.

The HF signals fed into the transit time measuring device 13 by the HF generator 11 are fed in part via a first directional coupler 35 into a measuring line 36 and partially decoupled from the latter via a further directional coupler 37 and by a detector serving as a level measuring device Circuit 38 detected. The measuring line 36 has a length of λ / 2. The HF generator 11 can generate different output frequencies controlled by the microcontroller 18. According to FIG. 4 successively different, gradually changing measuring frequencies of the transit time measuring device 13 are supplied. At a frequency with the wavelength λ, the highest level U _{R is} transmitted as a result of the resonance, the resonance frequency being the frequency f 2 _R. If the measuring line 16 changes, for example, as a result of the influence of moisture, then the resonance frequency shifts toward the frequency f1 _R , for example. The shift of the resonant frequency is a measure of changes in the transit time, with the evaluation in the microcontroller 18 takes place. This information is then used to compensate for corresponding propagation time changes in the other lines and calculated. A further detector circuit 39, which is likewise connected to the microcontroller 18, is connected directly to the line leading to the transit time measuring device 13. By level comparison of the two detector circuits 38, 39 can be calculated even more accurate compensation for the duration.

In principle, instead of directional couplers, other couplers can also be used for decoupling parts of the respective signal, such as Lange couplers, Rat Race couplers and Wilkinson dividers. Furthermore, the structural design of the six-port circuit may also differ from the embodiment and be executed, for example, according to the specified prior art.

In summary, in addition to the fluidic cylinder with a microwave measuring arrangement for detecting at least one parameter, the invention thus also relates to a method for detecting at least one parameter in a fluidic cylinder with the aid of a microwave measuring arrangement comprising a microwave coupling probe (19) in or on one Cylinder cover of the cylinder (21) for coupling a waveguide shaft in the adjacent cylinder space and for coupling and detection of a piston (23) in the cylinder (21) reflected waveguide wave, the microwave xoppelsonde (19) by an RF generator (11 ) is supplied with RF signals and the at least one parameter is detected by comparing the microwave coupling probe (19) forwarded outgoing RF signals with the generated from the reflected waveguide wave return RF signals by means of an evaluation, wherein parts of the leading and returning RF signals using at least e Ines coupling element (15) are coupled out and a phase and amplitude comparison by additive superimposition of the decoupled parts of the leading and returning RF signals with subsequent level measurement is carried out, and that the parameters are derived from the detected level values.

Claims (15)

A fluidic cylinder having a microwave measuring arrangement for detecting at least one parameter comprising a micro-wave coupling probe (19) in or on a cylinder cover of the cylinder (21) for coupling a waveguide shaft in the adjacent cylinder space and for coupling and detection of a Piston (23) in the cylinder (21) reflected waveguide wave, with an RF generator (11) for supplying the microwave coupling probe (19) with RF signals and with an evaluation device for detecting the at least one parameter by comparing the microwave coupling probe (19) forwarded outgoing RF signals with the generated from the reflected waveguide wave return RF signals, characterized in that at least a part of the evaluation device and the conductor tracks formed as HF lines from and to the evaluation device on a board (10) are arranged, and that on this board (10) has a transit time measuring device (13) for Erf Assignment of the board moisture and / or propagation speed of the RF signals is arranged, wherein the evaluation device is designed to correct the at least one detected parameter in dependence of the signals of the transit time measuring device (13). Fluidic cylinder according to claim 1, characterized in that the evaluation device comprises a phase and amplitude comparator (17) and a microcontroller (18) connected thereto. Fluidic cylinder according to claim 2, characterized in that the phase and amplitude comparator (17) comprises means for the additive superimposition of parts of the leading and returning RF signals and means for measuring the level of the superimposed signals. Fluidic cylinder according to claim 2 or 3, characterized in that the arranged on the board phase and amplitude comparator (17) is formed by conductor track elements and in particular as a six-port circuit (six-port device) is formed. A fluidic cylinder according to claim 4, characterized in that the six-port circuit (9) formed phase and amplitude comparator (17) has at least three 90-degree hybrid coupler (30-32) and a Wilkinson divider (33), wherein power and / or level measuring means (26-29) are provided for thereby formed by 90 ° offset and superimposed signals of the coupling probe (19) running back and from this returning RF signals with the microcontroller (18) for evaluation are connected. A fluidic cylinder according to claim 5, characterized in that the 90-degree hybrid coupler (30-32) are each four annularly connected to one another conductor track pieces of which each have a length of substantially λ / 4. Fluidic cylinder according to one of the preceding claims, characterized in that in the microwave coupling probe (19) leading conductor for the RF signals, a coupling member (15) for decoupling and / or additive superposition of a part of the trailing and a part of the Microwave coupling probe (19) returning RF signals is arranged. Fluidic cylinder according to claim 7, characterized in that the coupling member (15) as a directional coupler, Lange coupler, Wilkinson divider, 90grad hybrid coupler and / or Ra-race coupler is formed or at least one of them. Fluidic cylinder according to claim 7 or 8, characterized in that in one of the two the coupling member (15) with the phase and amplitude comparator (17) interconnects interconnects also designed as a conductor delay device (16) to compensate for the length of the interconnect between the coupling member (15) and the coupling probe (19) is arranged. Fluidic cylinder according to one of the preceding claims, characterized in that the transit time measuring device (13) consists essentially of conductor track pieces. Fluidic cylinder according to claim 10, characterized in that the transit time measuring device (13) comprises a measuring strip conductor piece (36) which has a coupling device (35) connected in particular to the HF generator (11) and a coupling device (37) coupled to a level measuring device (38), the measuring strip (36) preferably having a length of substantially λ / 2 or multiples of λ / 4. Fluidic cylinder according to claim 10 or 11, characterized in that the resonance measuring device (38) has a with the microcontroller (18) connected level measuring device, wherein the microcontroller (18) has means for stepwise frequency variation of the RF generator for detecting the respective resonance frequency , Fluidic cylinder according to one of claims 10 to 12, characterized in that a further level and / or resonance measuring device (39) connected to the microcontroller (18) is provided for detecting the RF power fed into the transit time measuring device (13). Fluidic cylinder according to one of the preceding claims, characterized in that a conductor connecting the RF generator (11) with the transit time measuring device (13) has a directional coupler (14) or another coupling link for coupling to the microwave coupling probe (19) Has RF signals. Fluidic cylinder according to one of the preceding claims, characterized in that the output signals of the HF generator (11) via a harmonic filter (12) are guided.

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